Storing multi-value custom product attribute

Question

I have a custom attribute for my products called 'car_model'. This is a multi-value field. Now I try to create a synchronization script to synchronize this data between Magento and another system. I start off with getting all products:

ini_set('display_errors',1);
require('app/Mage.php');
umask(0);
Mage::app();

$collection = Mage::getModel('catalog/product')->getCollection();

//fetch name and orig_price into data
$collection->addAttributeToSelect('name');
$collection->addAttributeToSelect('car_model');
$products = array();
foreach ($collection as $product) {
    $product = Mage::getModel('catalog/product')->load($product->getId());

    $product_id = $product->getId();
    $sku = $product->getSku();
    $product_name = $product->getData('name');
    $model = $product->getAttributeText('car_model');

    $products[$sku] = array('product_id'=>$product_id, 'model' => $model, 'modified' =>  false, 'product' => $product);
}

The $model variable contains the correct (text) values, so no problem there.

Then I do some hocus pocus to get what needs to be updated which resulted in the following code to save the products:

foreach($products as $sku=>$product) {
    if($product['modified']) {
        $attr = $product['product']->getResource()->getAttribute('car_model');
        //$models = array();
        foreach($product['model'] as $m) {
            $option_id = $attr->getSource()->getOptionId($m);
            //$models[$option_id] = $m;
            $product['product']->setData('car_model', $option_id);
    //       $product['product']->addAttributeUpdate('car_model', $option_id);
        }
       try {
            //$product['product']->setData('car_model', $models);
            //$product['product']->addAttributeUpdate('car_model', $option_id);
            //$product['product']->save();
            $product['product']->getResource()->saveAttribute($product['product'], 'car_model');
            echo "Set product " . $product['product_id'] . " " . $sku . " to " . implode(",",$product['model']) . "<br>";
       } catch(Exception $e) {
            echo 'failed updating product ' . $product['product_id'] . ' with message: ' . $e->getMessage() . '<br>';
       }
    }
}

As you can see from the commented lines I tried many different things, but it doesn't want to save the attributes correctly. From what I understand I need to call setData('car_model', $option_id) multiple times for all values. When I retrieve the product after saving though, I only get one value returned.

Furthermore, when I go to the backend, the values are not selected. I tried reindexing and clearing the cache (also emptying var/cache), but this doesn't make any difference. It seems like a basic thing to do, but somehow I don't get it to work. Any thoughts?

Answer 1

I believe the following should be sufficient:

$product->setData('car_model', $array_of_values)->save();

Although, if it's a standalone script, it won't allow you to save products unless you trick it into thinking you're in the backend by adding this at the top of your file:

Mage::app()->setCurrentStore(Mage_Core_Model_App::ADMIN_STORE_ID);